1. Field of the Invention
The present invention relates to an electrodynamic actuator of the type having a permanently magnetic stationary part that forms an air-core with a magnetic field therein, and an armature with a coil disposed in the air-core, the armature moving in the magnetic field in the air-core dependent on a drive current that is fed to the coil.
2. Description of the Prior Art
Electrodynamic actuators are often employed, for example, in the control of valves for regulating a gas flow in medical ventilators and other related devices.
One type of electrodynamic actuator, often referred to as a voice coil, has a permanently magnetic stationary part, designed to form an air-core (air gap). A relatively constant magnetic field exists in this air-core. An armature is arranged in this air-core. The armature carries a coil. By sending a driving current through the coil in the magnetic field, a force is imparted to the armature that is essentially proportional to the current.
In order to achieve a highly accurate and stable control it is necessary to provide the actuator with a viscous damping, i.e. a damping that is proportional to the speed of the armature. The damping may be either mechanical or electronic.
With electronic damping a determination of the speed is a key factor in achieving the possibility of high accuracy in the damping and thereby in the regulation of the moving part.